Re: [PATCH, libmpx, i386, PR driver/65444] Pass '-z bndplt' when building dynamic objects with MPX

[Ilya Enkovich <enkovich dot gnu at gmail dot com>]

2015-03-18 16:52 GMT+03:00 H.J. Lu <hjl.tools@gmail.com>:
> On Wed, Mar 18, 2015 at 6:41 AM, Ilya Enkovich <enkovich.gnu@gmail.com> wrote:
>> 2015-03-18 16:31 GMT+03:00 H.J. Lu <hjl.tools@gmail.com>:
>>> On Wed, Mar 18, 2015 at 6:24 AM, Ilya Enkovich <enkovich.gnu@gmail.com> wrote:
>>>> 2015-03-18 15:42 GMT+03:00 Richard Biener <richard.guenther@gmail.com>:
>>>>> On Wed, Mar 18, 2015 at 1:25 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>>> On Wed, Mar 18, 2015 at 5:13 AM, Ilya Enkovich <enkovich.gnu@gmail.com> wrote:
>>>>>>> 2015-03-18 15:08 GMT+03:00 H.J. Lu <hjl.tools@gmail.com>:
>>>>>>>> On Wed, Mar 18, 2015 at 5:05 AM, Ilya Enkovich <enkovich.gnu@gmail.com> wrote:
>>>>>>>>> 2015-03-18 15:02 GMT+03:00 H.J. Lu <hjl.tools@gmail.com>:
>>>>>>>>>> On Wed, Mar 18, 2015 at 4:56 AM, Ilya Enkovich <enkovich.gnu@gmail.com> wrote:
>>>>>>>>>>> Hi,
>>>>>>>>>>>
>>>>>>>>>>> This patch fixes PR target/65444 by passing '-z bndplt' to linker when appropriate.  Bootstrapped and tested on x86_64-unknown-linux-gnu.  Will commit it to trunk in a couple of days if no objections arise.
>>>>>>>>>>>
>>>>>>>>>>> Thanks,
>>>>>>>>>>> Ilya
>>>>>>>>>>> --
>>>>>>>>>>> gcc/
>>>>>>>>>>>
>>>>>>>>>>> 2015-03-18  Ilya Enkovich  <ilya.enkovich@intel.com>
>>>>>>>>>>>
>>>>>>>>>>>         PR driver/65444
>>>>>>>>>>>         * config/i386/linux-common.h (MPX_SPEC): New.
>>>>>>>>>>>         (CHKP_SPEC): Add MPX_SPEC.
>>>>>>>>>>>
>>>>>>>>>>> libmpx/
>>>>>>>>>>>
>>>>>>>>>>> 2015-03-18  Ilya Enkovich  <ilya.enkovich@intel.com>
>>>>>>>>>>>
>>>>>>>>>>>         PR driver/65444
>>>>>>>>>>>         * configure.ac: Add check for '-z bndplt' support
>>>>>>>>>>>         by linker. Add link_mpx output variable.
>>>>>>>>>>>         * libmpx.spec.in (link_mpx): New.
>>>>>>>>>>>         * configure: Regenerate.
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> diff --git a/gcc/config/i386/linux-common.h b/gcc/config/i386/linux-common.h
>>>>>>>>>>> index 9c6560b..dd79ec6 100644
>>>>>>>>>>> --- a/gcc/config/i386/linux-common.h
>>>>>>>>>>> +++ b/gcc/config/i386/linux-common.h
>>>>>>>>>>> @@ -59,6 +59,11 @@ along with GCC; see the file COPYING3.  If not see
>>>>>>>>>>>   %:include(libmpx.spec)%(link_libmpx)"
>>>>>>>>>>>  #endif
>>>>>>>>>>>
>>>>>>>>>>> +#ifndef MPX_SPEC
>>>>>>>>>>> +#define MPX_SPEC "\
>>>>>>>>>>> + %{mmpx:%{fcheck-pointer-bounds:%{!static:%:include(libmpx.spec)%(link_mpx)}}}"
>>>>>>>>>>> +#endif
>>>>>>>>>>> +
>>>>>>>>>>>  #ifndef LIBMPX_SPEC
>>>>>>>>>>>  #if defined(HAVE_LD_STATIC_DYNAMIC)
>>>>>>>>>>>  #define LIBMPX_SPEC "\
>>>>>>>>>>> @@ -89,5 +94,5 @@ along with GCC; see the file COPYING3.  If not see
>>>>>>>>>>>
>>>>>>>>>>>  #ifndef CHKP_SPEC
>>>>>>>>>>>  #define CHKP_SPEC "\
>>>>>>>>>>> -%{!nostdlib:%{!nodefaultlibs:" LIBMPX_SPEC LIBMPXWRAPPERS_SPEC "}}"
>>>>>>>>>>> +%{!nostdlib:%{!nodefaultlibs:" LIBMPX_SPEC LIBMPXWRAPPERS_SPEC "}}" MPX_SPEC
>>>>>>>>>>>  #endif
>>>>>>>>>>> diff --git a/libmpx/configure.ac b/libmpx/configure.ac
>>>>>>>>>>> index fe0d3f2..3f8b50f 100644
>>>>>>>>>>> --- a/libmpx/configure.ac
>>>>>>>>>>> +++ b/libmpx/configure.ac
>>>>>>>>>>> @@ -40,7 +40,18 @@ AC_MSG_RESULT($LIBMPX_SUPPORTED)
>>>>>>>>>>>  AM_CONDITIONAL(LIBMPX_SUPPORTED, [test "x$LIBMPX_SUPPORTED" = "xyes"])
>>>>>>>>>>>
>>>>>>>>>>>  link_libmpx="-lpthread"
>>>>>>>>>>> +link_mpx=""
>>>>>>>>>>> +AC_MSG_CHECKING([whether ld accepts -z bndplt])
>>>>>>>>>>> +echo "int main() {};" > conftest.c
>>>>>>>>>>> +if AC_TRY_COMMAND([${CC} ${CFLAGS} -Wl,-z,bndplt -o conftest conftest.c 1>&AS_MESSAGE_LOG_FD])
>>>>>>>>>>> +then
>>>>>>>>>>> +    AC_MSG_RESULT([yes])
>>>>>>>>>>> +    link_mpx="$link_mpx -z bndplt"
>>>>>>>>>>> +else
>>>>>>>>>>> +    AC_MSG_RESULT([no])
>>>>>>>>>>> +fi
>>>>>>>>>>>  AC_SUBST(link_libmpx)
>>>>>>>>>>> +AC_SUBST(link_mpx)
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Without -z bndplt, MPX won't work correctly.  We should always pass -z bndplt
>>>>>>>>>> to linker.  If linker doesn't support it, ld will issue a warning, not
>>>>>>>>>> error and users
>>>>>>>>>> will know their linker is too old.  When they update linker, they don't have to
>>>>>>>>>> rebuild GCC.
>>>>>>>>>
>>>>>>>>> If ld issues a warning instead of an error, then configure test passes
>>>>>>>>> and we pass '-z bndplt' to linker.
>>>>>>>>>
>>>>>>>>
>>>>>>>> Can you verify it with an older linker? The unknown XXX in -z XXX is always
>>>>>>>> warned and ignored in Linux linker.  If testing it on Linux always passes,
>>>>>>>> it is useless.
>>>>>>>
>>>>>>> Old ld issues a warning:
>>>>>>>
>>>>>>> ld: warning: -z bndplt ignored.
>>>>>>
>>>>>> Does configure test pass?
>>>>>>
>>>>>>> But gold issues an error:
>>>>>>>
>>>>>>> ld.gold: bndplt: unknown -z option
>>>>>>> ld.gold: use the --help option for usage information
>>>>>>
>>>>>> If gold is used, MPX won't work.  What should we do here?
>>>>>> Should we hardcode -fuse-ld=bfd for MPX?
>>>>>
>>>>> Is MPX disabled when the host linker is gold and gld isn't available?
>>>>
>>>> No. You may use MPX with gold and old ld but you would loose passed
>>>> bounds when make a call via plt.
>>>>
>>>
>>> If gold is default linker, the configure test will fail and we never pass
>>> -z bndplt to linker even if ld.bfd is available and ld.gold is fixed later.
>>> I'd rather always pass -z bndplt to ld.
>>
>> If gold is used and it doesn't support '-z bndplt' then it doesn't
>> mean user can't use MPX.
>
> They can use -fuse-ld=bfd to select bfd linker if gold fails to generate
> proper MPX binary.

Which is a weird thing to do just to have a warning instead of an
error. You don't guarantee MPX PLT generation by always passing '-z
bndplt' but remove an opportunity to use gold at all. With current
check you may use any linker and manually provide additional options
if you want to.

Ilya

>
>
> --
> H.J.